Summary

In laboratory, growth chamber, micro-plot and small-plot field trials, 53 copper-free preparations (CFPs) were examined for their potential to control potato late blight (PLB) caused by Phytophthora infestans (PI). In-vitro, 43% of the CFP inhibited the germination of sporangia or the mycelial growth of the pathogen completely. In growth chamber trials, 21% of them reduced PI foliar blight of tomato seedlings by at least 80%. In contrast, in small-plot field trials with potatoes under practice like applications, none of the CFPs sufficiently controlled the disease. Even in micro-plot field trials with applications twice a week the efficacies did not exceed 60%. With in-vitro tests we showed that the reason for the insufficient performance of the CFPs was due to their lack of persistence and rainfastness. However, applications of copper fungicides with low rates according to the decision support system Bio-PhytoPRE resulted in a good control of late blight. We recommend using this strategy until CFPs are developed for practise application.